The MIUI ROM is heavy. I noticed severe slowing down in places. I did not use it for more than a few days though. So it could be that cleaning up the system a bit, might have helped.The MIUI looks great, is pleasure to use with great looks, features and a similarity everywhere. But its far too removed from the android experience.
Link on needrom: http://www.needrom.com/download/miui-os-for-v889s-v807/